The present invention relates to a differential impulse conveyor for moving goods along a conveyor tray. More particularly, this invention relates to an improved drive mechanism which utilizes an electrically powered linear motor for powering movement of the differential impulse conveyor tray with respect to a conveyor base. A related invention involves a linear connector for interconnecting a stationary member and a movable member, with the connector being pivotally connected to one of the members. The connector includes a linear bearing for achieving straight line motion rather than arcuate motion of the movable member.
Various types of conveyors are available which each employ an elongate, slightly downwardly inclined tray or pan having a planar surface for transporting goods thereon. These types of conveyors are preferred in various industries since the goods being transported along the tray need only engage a unitary tray during the conveying operation, and since the tray may be easily cleaned. Conveyors of this type have been used for decades and include those commonly referred to as reciprocating conveyors, shaker conveyors, or vibratory conveyors.
Differential impulse conveyors may also use a slightly downwardly inclined tray, but alternatively may use a horizontal tray or slightly upwardly inclined tray. Differential impulse conveyors, which are sometimes referred to as linear motion conveyors, are operationally distinguishable from vibratory conveyors because the tray is moved slowly forward to convey the goods with respect to the tray, and then is moved rearward at a high return speed so that the goods slide along the tray, thereby effectively transporting the goods along the conveyor tray. A significant advantage of differential impulse conveyors is that these conveyors do not tend to damage fragile goods. Moreover, a differential impulse conveyor does not require gravity to move goods along the tray, and accordingly the tray supporting surface may be horizontal or may even be inclined upwardly. Accordingly, differential impulse conveyors have gained increased acceptance in recent years.
The drive mechanism for a differential impulse conveyor generates repeated acceleration and deceleration of the tray. Since the forward acceleration is less than the rearward acceleration, the goods move with the tray when the tray moves forward, and slide with respect to the tray when the tray moves rearward. Early types of drive mechanisms for achieving this motion in a differential impulse conveyor included a plurality of weights which were moved back and forth to obtain the desired movement of the tray. These inertia drive systems impart high loads to the conveyor support structure or base, and thus typically require a heavy and expensive support structure for the conveyor. These inertia drive systems undesirably require a fair amount of startup time before the motor driving the weights causes the tray to move in its desired manner, and similarly result in tray movement for a period of time after the drive motor is deenergized. Also, these inertia drive mechanisms are costly and complicated, and frequently have high maintenance costs.
Another type of drive mechanism for powering a differential impulse conveyor utilizes a power source which cooperates with mechanical components which directly move the tray. One such arrangement, as disclosed in U.S. Pat. No. 5,351,807, employs an angled universal drive and a speed reducer to achieve the desired tray movement. Other drive systems for powering a differential impulse conveyor are disclosed in U.S. Pat. No. 5,794,757. One drive mechanism recently introduced to the marketplace employs a plurality of eccentrically mounted pulleys. A crank arm interconnects one of the pulleys and a tray support arm to drive the conveyor tray slowly forward and then quickly backward. The systems disclosed in the above two patents have significant advantages over inertia drive systems for powering a differential impulse conveyor. These drive systems have the ability to substantially instantaneously achieve the desired tray motion when the drive unit is started, and similarly instantaneously stop the tray motion when the drive unit is stopped. This is a significant advantage of these drive units compared to the inertia drive mechanisms, and allows the differential impulse conveyor to be reliably used for cross-feed applications. The size and expense of these latter described drive systems, as well as the number of moving parts, nevertheless restricts the acceptability of differential impulse conveyors, particularly in applications wherein the size and cost of the drive system are significant factors to the customer.
The disadvantages of the prior art are overcome by the present invention. An improved differential impulse conveyor with a linear drive mechanism is hereinafter disclosed. The drive mechanism has few moving parts, and in many applications requires less space and cost than other drive mechanisms. An improved connector is also disclosed for pivotally interconnecting a stationary member and a member movable with respect to the stationary member such that the movable member reciprocates in a straight line path rather than in an arcuate path.
A differential impulse conveyor includes a tray movable in a forward direction to move with the goods and in a backward direction to slide goods along the tray. An electrically powered linear motor moves the tray in the forward direction and in the backward direction. The linear motor has an armature linearly movable with respect to a stator in a reciprocating manner to move the tray. A pair of tray support arms interconnect a conveyor base and the tray. The armature of the linear motor may be connected to either one of the tray support arms or directly to the tray.
In a preferred embodiment of the invention, each tray support member is pivotally connected to a lower end to the conveyor base and is pivotally connected at an upper end to the tray. The electrically powered motor stator may have a plate-like configuration, and the armature may have a similar configuration. Electrical power supplied to the motor thus linearly moves the armature with respect to the stator, and thereby moves the tray with respect to the base. For differential impulse conveyors with relatively large trays, a counterweight may be provided movable in a backward direction during forward movement of the tray and in a forward direction during backward movement of the tray.
A connector for interconnecting a stationary member and a movable member linearly movable in a straight line path is also provided. A pivot at one end of the connector is connected to one of the stationary and movable members. A specially designed curved end surface on the connector and a specially designed curved contact surface on the other of the stationary and movable member result in rolling engagement of engaging curved surfaces to result in straight line travel of the movable member.
It is an object of the present invention to provide an improved differential impulse conveyor utilizing an electrically powered linear motor to move the tray in a forward direction and in a backward direction. A related object of the invention is to increase the acceptability of differential impulse conveyors in various applications by providing a conveyor drive mechanism which is highly reliable and has a relatively low cost.
It is an object of a related invention to provide a connector for interconnecting a stationary member and a movable member, with the connector being pivotally connected at one end to one of the stationary member and movable member. The opposing end of the connector has a curved end surface with a radius positioned along the pivot axis. A curved contact surface is provided on the other of the stationary member and the movable member, which contact surface has a radius twice that of the end surface. This curved contact surface engages the curved end surface to provide for linear motion of the movable member with respect to the stationary member.
It is a feature of the invention to provide a controller for regulating the linear drive motor of a differential impulse conveyor, such that the cycle rate of the linear motor is controlled to regulate the travel speed of the product moving along the reciprocating tray. Another feature of the present invention is that the linear motor conveyor is well adapted for use to drive a differential impulse conveyor tray forward and backward, with the tray being supported on a pair of arms pivotally connected to the conveyor tray. High reliability for the conveyor may be enhanced by eliminating or at least substantially reducing the number of linear bearings which guide tray movement with respect to the base in both the forward and backward directions.
Another significant feature of this invention is that the number of movable parts required to drive the tray of a differential impulse conveyor may be reduced compared to prior art drive mechanisms. Both the size and the cost of the drive system for powering the differential impulse conveyor may also be reduced, thereby significantly increasing the applications in which a differential impulse conveyor is a preferred type of transport system for the goods.
Yet another feature of the invention is that differential impulse conveyor may include a pair of supports each forming an improved linear bearing with a specially designed contact surface in the base of the conveyor, such that each support may be pivotally connected to the tray while the axis of this pivotal connection remains at the same elevation during the forward and rearward movement of the tray.
An advantage of the present invention is that another linear drive motor may be used to power a counterweight which opposes movement of the tray. Alternatively, a linkage mechanism may be provided so that the counterweight and the tray are driven by the same linear motor, with a counterweight moving in the opposite direction of the tray.
Yet another advantage of this invention is that the linear motor drive system is able to substantially immediately obtain the desired motion of the conveyor tray upon activation of the linear motor, and similarly stops tray motion substantially immediately upon deactivation of the linear motor, such that the conveyor is well suited for various applications.
Another significant advantage of the present invention is that the cost of linear motors is relatively low. The selected linear motor may either utilize permanent magnets or an electrical coil or winding on both the stator and the armature. A linear motor with a stator coil encircling an armature may be used. Alternatively, a linear motor may have either a flat plate stator and a flat plate armature, or a curved plate stator and a curved plate armature.
These and further objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.